If you think that most cacti are leafless plants, think again: scientists had just discovered that all cacti actually have leaves, though most are small enough that you'd need a microscope to see them:

Leaf sizes ranged from 30 to 2310 micrometers. A single micrometer is equal to one millionth of a meter or just .00003937 inch, so the documented cactus leaves may very well be the world’s smallest.